Message ID | 20231025-delay-verw-v3-0-52663677ee35@linux.intel.com |
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Headers |
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Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <peterz@infradead.org>, Josh Poimboeuf <jpoimboe@kernel.org>, Andy Lutomirski <luto@kernel.org>, Jonathan Corbet <corbet@lwn.net>, Sean Christopherson <seanjc@google.com>, Paolo Bonzini <pbonzini@redhat.com>, tony.luck@intel.com, ak@linux.intel.com, tim.c.chen@linux.intel.com Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, Alyssa Milburn <alyssa.milburn@linux.intel.com>, Daniel Sneddon <daniel.sneddon@linux.intel.com>, antonio.gomez.iglesias@linux.intel.com, Pawan Gupta <pawan.kumar.gupta@linux.intel.com>, Alyssa Milburn <alyssa.milburn@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Dave Hansen <dave.hansen@intel.com>, Nikolay Borisov <nik.borisov@suse.com> Subject: [PATCH v3 0/6] Delay VERW Message-ID: <20231025-delay-verw-v3-0-52663677ee35@linux.intel.com> X-B4-Tracking: v=1; b=H4sIAH19OWUC/2XMSw6CMBSF4a2Qji3pSyiO3IdxgO2t3ASLabFCC Hu3wQnG4fmT8y0kQkCI5FQsJEDCiIPPQx4KYrrW34GizZsIJiRnnFMLfTvTBOFNLVO1anR1E0a SfHgGcDht2IWQay4dxnEI86YnvvUvJNgeSpwyapw7KtZUUlT23KN/TSX6EfrSDI8NS2IPqB9AZ MBxrblUzGhW/wPrun4A7q9Tae0AAAA= X-Mailer: b4 0.12.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-0.8 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.vger.email Precedence: bulk List-ID: <linux-kernel.vger.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (agentk.vger.email [0.0.0.0]); Wed, 25 Oct 2023 13:53:35 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1780762383247868757 X-GMAIL-MSGID: 1780762383247868757 |
Series |
Delay VERW
|
|
Message
Pawan Gupta
Oct. 25, 2023, 8:52 p.m. UTC
v3:
- Use .entry.text section for VERW memory operand. (Andrew/PeterZ)
- Fix the duplicate header inclusion. (Chao)
v2: https://lore.kernel.org/r/20231024-delay-verw-v2-0-f1881340c807@linux.intel.com
- Removed the extra EXEC_VERW macro layers. (Sean)
- Move NOPL before VERW. (Sean)
- s/USER_CLEAR_CPU_BUFFERS/CLEAR_CPU_BUFFERS/. (Josh/Dave)
- Removed the comments before CLEAR_CPU_BUFFERS. (Josh)
- Remove CLEAR_CPU_BUFFERS from NMI returning to kernel and document the
reason. (Josh/Dave)
- Reformat comment in md_clear_update_mitigation(). (Josh)
- Squash "x86/bugs: Cleanup mds_user_clear" patch. (Nikolay)
- s/GUEST_CLEAR_CPU_BUFFERS/CLEAR_CPU_BUFFERS/. (Josh)
- Added a patch from Sean to use CFLAGS.CF for VMLAUNCH/VMRESUME
selection. This facilitates a single CLEAR_CPU_BUFFERS location for both
VMLAUNCH and VMRESUME. (Sean)
v1: https://lore.kernel.org/r/20231020-delay-verw-v1-0-cff54096326d@linux.intel.com
Hi,
Legacy instruction VERW was overloaded by some processors to clear
micro-architectural CPU buffers as a mitigation of CPU bugs. This series
moves VERW execution to a later point in exit-to-user path. This is
needed because in some cases it may be possible for kernel data to be
accessed after VERW in arch_exit_to_user_mode(). Such accesses may put
data into MDS affected CPU buffers, for example:
1. Kernel data accessed by an NMI between VERW and return-to-user can
remain in CPU buffers (since NMI returning to kernel does not
execute VERW to clear CPU buffers).
2. Alyssa reported that after VERW is executed,
CONFIG_GCC_PLUGIN_STACKLEAK=y scrubs the stack used by a system
call. Memory accesses during stack scrubbing can move kernel stack
contents into CPU buffers.
3. When caller saved registers are restored after a return from
function executing VERW, the kernel stack accesses can remain in
CPU buffers(since they occur after VERW).
Although these cases are less practical to exploit, moving VERW closer
to ring transition reduces the attack surface.
Overview of the series:
Patch 1: Prepares VERW macros for use in asm.
Patch 2: Adds macros to 64-bit entry/exit points.
Patch 3: Adds macros to 32-bit entry/exit points.
Patch 4: Enables the new macros.
Patch 5: Uses CFLAGS.CF for VMLAUNCH/VMRESUME selection.
Patch 6: Adds macro to VMenter.
Below is some performance data collected with v1 on a Skylake client
compared with previous implementation:
Baseline: v6.6-rc5
| Test | Configuration | Relative |
| ------------------ | ---------------------- | -------- |
| build-linux-kernel | defconfig | 1.00 |
| hackbench | 32 - Process | 1.02 |
| nginx | Short Connection - 500 | 1.01 |
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
Pawan Gupta (5):
x86/bugs: Add asm helpers for executing VERW
x86/entry_64: Add VERW just before userspace transition
x86/entry_32: Add VERW just before userspace transition
x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key
KVM: VMX: Move VERW closer to VMentry for MDS mitigation
Sean Christopherson (1):
KVM: VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH
Documentation/arch/x86/mds.rst | 39 ++++++++++++++++++++++++++----------
arch/x86/entry/entry.S | 16 +++++++++++++++
arch/x86/entry/entry_32.S | 3 +++
arch/x86/entry/entry_64.S | 11 ++++++++++
arch/x86/entry/entry_64_compat.S | 1 +
arch/x86/include/asm/cpufeatures.h | 2 +-
arch/x86/include/asm/entry-common.h | 1 -
arch/x86/include/asm/nospec-branch.h | 27 ++++++++++++++-----------
arch/x86/kernel/cpu/bugs.c | 15 ++++++--------
arch/x86/kernel/nmi.c | 2 --
arch/x86/kvm/vmx/run_flags.h | 7 +++++--
arch/x86/kvm/vmx/vmenter.S | 9 ++++++---
arch/x86/kvm/vmx/vmx.c | 10 ++++++---
13 files changed, 99 insertions(+), 44 deletions(-)
---
base-commit: 05d3ef8bba77c1b5f98d941d8b2d4aeab8118ef1
change-id: 20231011-delay-verw-d0474986b2c3
Best regards,